This invention relates to a viewing device for use in conjunction with a bubble level and, in particular, to a device to enable the user to accurately read a bubble level from any off axis position under adverse lighting conditions.
It is well known in the art that a serious lack of contrast is present when a worker is attempting to read a bubble level indicator as conventionally found in a spirit level or the like. Most levels of this nature commonly contain a bubble column or chamber constructed with alcohol, chloroform, ether or other such colorless liquid which is difficult to discern when the lighting is less than optimum. Adverse lighting conditions can involve overexposure of the bubble region due to direct intense sunlight or more typically insufficient lighting owing to poor weather or a dark confined working area. Working in a confined space can also increase the chances of making a reading error in that the level user is oftentimes forced to view the instrument at less than an optimum reading angle.
As exemplified by U.S. Pat. No. 2,344,241 to Flint, some attempts have been made towards improving the lighting in and about the bubble region of the level, however, little consideration has been given to the problems associated with reading the level at an undesirable off axis angle. In Flint the level is provided with both a lamp and luminescent strips that are applied about the borders of the bubble chamber.